It was the working class.
I think it is the Industrial Revolution
The growing social class of factory workers became known as the proletariat. This term refers to the working class who sell their labor for wages and do not own the means of production.
Marx called such workers proletarians. He called the social class made up of such workers the proletariat.
Working Class
the bourgeoisie
Unions allowed factory workers to make good wages which led to the growth of the middle class.
In the early 1900s in New England, the social classes were typically divided into the upper class, which consisted of wealthy industrialists, businessmen, and elite families; the middle class, comprising professionals, skilled workers, and small business owners; and the working class, made up of laborers, factory workers, and immigrants. Social mobility was limited during this time, with individuals often remaining within their respective class boundaries.
Industrialism led to the creation of distinct social classes, as wealth became concentrated among industrialists and business owners while many workers toiled in poor conditions for low wages. This resulted in a widening gap between the rich and the poor, leading to social inequality and class conflicts. Additionally, industrialism also led to the emergence of a middle class comprised of skilled workers and professionals.
Factory workers.
Urbanization developed new social classes such as the working class, middle class, and urban poor. The working class typically comprised factory workers and laborers, while the middle class included professionals and managers. The urban poor often lived in overcrowded and unsanitary conditions, facing economic hardship.
The Middle Class
During the Elizabethan era, English society was divided into four main social classes: the nobility, the gentry, the merchant class, and the laboring class. The nobility held the highest social rank, followed by the gentry who were wealthy landowners. Merchants were successful businessmen who often became wealthy, and the laboring class included skilled and unskilled workers who were at the bottom of the social hierarchy.